| Sacrificial coating for fluoride ion cleaning -> Monitor Keywords |
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Sacrificial coating for fluoride ion cleaningRelated Patent Categories: Stock Material Or Miscellaneous Articles, Composite (nonstructural Laminate), Of MetalSacrificial coating for fluoride ion cleaning description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070087208, Sacrificial coating for fluoride ion cleaning. Brief Patent Description - Full Patent Description - Patent Application Claims
RELATED APPLICATIONS [0001] This application claims priority to Singapore Patent Application No. 200506795-4, filed Oct. 18, 2005. BACKGROUND OF THE INVENTION [0002] This invention relates to a method for repairing defects in gas turbine engine components and, more particularly, to utilizing a protective coating to resist inter-granular attack during chemical cleaning. [0003] Conventional gas turbine engines include components such as high and low pressure turbine vanes that operate for extended periods of time under relatively harsh conditions. Under such conditions, the gas turbine engine components may incur damage from erosion, creep, and high cycle fatigue that results in defects such as cracks. Typically, the defects can be repaired to extend the service life of the gas turbine engine component. [0004] Conventional repair methods include cleaning the defect to remove oxidation and particles that may hamper the repair. After the cleaning, a braze material such as a braze filler powder is applied near the defect. The gas turbine engine component is then heated to melt the braze material and fill in the defect portion. [0005] Conventional cleaning processes include using hydrogen fluoride gas to reduce oxidation on the defect surface and transform undesired particles into volatile fluorides that are then carried away by hydrogen gas. Disadvantageously, the hydrogen fluoride gas preferentially attacks grain boundaries of a metallic microstructure of the gas turbine engine component, which may undesirably weaken the gas turbine engine component, lead to unsuccessful repair, and result in scrappage of the component. [0006] Accordingly, there is a need for a method of cleaning gas turbine engine component defects while minimizing the possibility of inter-granular boundary attack. SUMMARY OF THE INVENTION [0007] The present invention provides a method of repairing a defect in a gas turbine engine component. The defect has a defect surface that includes grain boundaries. The defect is exposed to a chemically reducing gas to clean the defect surface of undesired particles and oxidation. Before the cleaning, a protective coating is applied to the defect surface to protect the grain boundaries from chemical attack. The protective coating functions as a sacrificial layer such that the chemically reducing gas preferentially attacks the protective coating rather than the grain boundaries. [0008] The example method of repairing a defect in a gas turbine engine component therefore provides the benefit of minimizing inter-granular attack during chemical cleaning. BRIEF DESCRIPTION OF THE DRAWINGS [0009] The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows. [0010] FIG. 1 shows an example gas turbine engine component having a defect. [0011] FIG. 2 shows a closer view of the defect of the gas engine component shown in FIG. 1. [0012] FIG. 3 illustrates steps of a gas turbine engine component repair process. [0013] FIG. 4 illustrates a chemically reducing gas diffusing through a protective coating that is applied to a defect surface of a crack of a gas turbine engine component. [0014] FIG. 5 shows the chemically reducing gas depleting the protective coating shown in FIG. 4. [0015] FIG. 6 shows the defect surface of a gas turbine engine component after the cleaning process. [0016] FIG. 7 shows the defect after a brazing process. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT [0017] FIG. 1 illustrates selected portions of an example gas turbine engine component 10 such as a turbine vane. In this example, the gas turbine engine component 10 includes a defect portion 12, such as a microscopic crack. [0018] FIG. 2 shows the defect portion 12 illustrated in FIG. 1. The defect portion 12 includes a crack 14 having a crack surface 16 with undesired impurities such as an oxide scale 18 and particles 20. The particles 20 may be, for example, titanium or aluminum based which, and under some conditions may form undesired oxides. [0019] FIG. 3 illustrates steps used to repair the crack 14. Generally, the method includes a coating step 22, a cleaning step 24, and a brazing step 26. The crack 14 is coated in step 22 to resist inter-granular attack during the cleaning process. The crack 14 is then exposed to a cleaning gas such as hydrogen fluoride in step 24 to remove the oxidation scale 18 and undesired particles 20. Finally, in step 26 the crack 14 is filled with a braze material and heated in a known manner to repair the crack 14. These steps will be described in more detail below. Continue reading about Sacrificial coating for fluoride ion cleaning... Full patent description for Sacrificial coating for fluoride ion cleaning Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Sacrificial coating for fluoride ion cleaning patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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